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Planetary News: Near Earth Objects (2004)

What to Do When the Big One Heads Our Way?

Apparent Close Call by Asteroid Stirs Debate

By Amir Alexander
27 February 2004

It was the evening of January 13, 2004, and Richard Miles was alarmed. A British amateur astronomer specializing in tracking Near Earth Objects (NEO’s) , he had just logged on to the NEO Confirmation Page of the Minor Planet Center website, where professional observatories post the latest detections of space rocks. One of the objects reported, designated AL00667, struck him as incredible: according to the web page, over the next 24 hours the object was to increase in brightness 40 times over. Like bright headlights on a dark road, this could mean only one thing: AL00667 was heading straight towards us!

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As it turned out AL00667, later designated 2004AS1, was harmless. Observations on following nights revealed that it was much larger and much further away than was initially suspected. It passed the Earth at a safe distance, giving our home planet a wide 8 million miles berth. But what occurred in the hours between the object’s first detection and the time late that night when it was determined that it was not going to impact the Earth has become the object of a fierce controversy in the NEO community.

According to a New York Times report, it all began when Dr. Timothy Spahr of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics was sifting through the latest observations from LINEAR – a NEO search using an automated telescope located in New Mexico. Spahr selected a few of the more interesting objects, and ran them through a computer program that calculates possible orbits, and posted the results on the web. He did not notice that the projected orbit of one of the bodies would take it directly through the Earth.

Others, however, did notice. In Britain, Miles began scanning the patch of sky where the asteroid would appear if it were heading towards Earth. In Germany, Amateur astronomer Reiner Stoss set astronomers chat rooms around the world buzzing, when he pointed out the implications of the posted orbit.

Professional astronomers also began to take note. Late that night Dr. Steven Chesley of the Near Earth Objects office at the Jet Propulsion Laboratory managed to reach Spahr, who until that time was unaware of the storm he had conjured. Together they calculated that the chances of the asteroid hitting the Earth were between 10 and 40 percent.

What was needed was an additional observation that would establish whether 2004AS1 was headed towards the Earth or not. Unfortunately, the skies over much of Europe and the United States were cloudy that day, blocking out the night sky for many professional and amateur star-gazers. Eventually, at 3:30am, amateur astronomer Brian Warner at the Palmer Divide Observatory in Colorado looked at the patch of sky where the rock would have been if it was on a collision course with the Earth. He found nothing, and the “emergency” passed.

But while 2004AS1 sailed by the Earth without causing a ripple, the events of the night of January 14 stirred up a storm in their wake. The main, and still unresolved, issue at stake is simple: what should astronomers do if they discover a space object that appears likely to strike the Earth within hours or days?

Some astronomers, including Clark Chapman of the Southwest Research Institute, and David Morrison, chair of the International Astronomical Union’s Working Group on Near Earth Objects, were extremely concerned that night ,and were beginning to consider when they should raise the alarm with government authorities. “I would not have been comfortable with being quiet through the next morning” Chapman told the New York Times.

Many others disagreed. “They completely misread the situation,” Benny Peiser of the Liverpool John Moores University told the BBC. “There was plenty of time to get other observers on the job.” “I find it incredible that such action was contemplated after just four observations” seconded Brian Marsden, director of the Minor Planets Center. “That is just not enough to yield a sensible orbit.” Donald Yeomans, head of the Near Earth Objects program at NASA also argued for caution, telling the New York Times that another set of observations confirming the collision path would be required before scientists could reasonably consider notifying the authorities.

The upshot of this debate is that it has become clear that there are currently no set procedures in place to deal with such an event. While NASA’s “Spaceguard” program is designed to detect objects orbiting near the Earth, the program’s focus is only on large rocks, over 1 kilometer in length, and on long lead times of months and years before an impact could be possible. There is as yet no program or plan to deal with smaller objects that may slam into the Earth with advance notice of only hours or days.

When on the night of January 13 it seemed possible that a large space rock was hurtling towards the Earth, it was not at all clear to astronomers what should be done about it, and who, if anyone, should be notified. One likely outcome of the storm is that when another space rock appears to have the Earth in its cross-hairs, astronomers will be prepared.